/* Hawk - A Component Based Test Framework
 *
 * Copyright (C) 2010 http://code.google.com/p/hawk-framework/
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License. 
 */
package org.hawk.applications.finder.swing.matching;

public class Correlation {
	
	public static double getPearsonCorrelation(byte[] scores1, byte[] scores2){
        
		double result = 0;
        double sum_sq_x = 0;
        double sum_sq_y = 0;
        double sum_coproduct = 0;
        double mean_x = scores1[0];
        double mean_y = scores2[0];
        
        for(int i=2;i<scores1.length+1;i+=1){
            double sweep =Double.valueOf(i-1)/i;
            double delta_x = scores1[i-1]-mean_x;
            double delta_y = scores2[i-1]-mean_y;
            sum_sq_x += delta_x * delta_x * sweep;
            sum_sq_y += delta_y * delta_y * sweep;
            sum_coproduct += delta_x * delta_y * sweep;
            mean_x += delta_x / i;
            mean_y += delta_y / i;
        }
        
        double pop_sd_x = (double) Math.sqrt(sum_sq_x/scores1.length);
        double pop_sd_y = (double) Math.sqrt(sum_sq_y/scores1.length);
        double cov_x_y = sum_coproduct / scores1.length;
        
        result = cov_x_y / (pop_sd_x*pop_sd_y);
        
        return result;
        
    }
	
}